An uplink MU-MIMO system supports multiple users using a pre-coding or post-coding scheme for each user in an uplink multi-antenna environment.
In the uplink multi-antenna environment, multiple users may be supported by uplink Orthogonal Multiple Access (OMA) or uplink Non-Orthogonal Multiple Access (NOMA). When the number of multiple users or the total number of antennas of multiple users is smaller than the number of antennas in a Base Station (BS), the multiple users are supported by uplink OMA. In other words, spatial resources are divided for the users in uplink OMA. Accordingly, if a BS uses a post-coding scheme based on zero-forcing beamforming in an uplink environment, there is no interference between uplink users. However, the number of users supported simultaneously (e.g., the number of simultaneous users) is limited by the number of BS antennas, that is, the number of antennas at a receiver. As a result, communication capacity (e.g., channel capacity or sum capacity) is restricted. Zero-forcing beamforming is a scheme of cancelling interference between users by steering a beam for each user in an orthogonal direction to a beam for another user.
If the number of multiple users, that is, the total number of antennas of multiple users is equal to or larger than the number of antennas at a receiver (or a BS), the multiple users are supported by uplink NOMA. As many users as or more users than the number of BS antennas may be supported simultaneously in the uplink NOAM scheme. However, if the BS uses a post-coding scheme, orthogonality is not maintained between users. The resulting interference between users may decrease communication capacity.
Although a NOMA scheme of sharing one beam among a plurality of users has been proposed for a downlink environment, this was for applying only a pre-coding scheme in the downlink environment. Therefore, this NOMA scheme is not viable for the uplink environment.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.